1. Field of the Invention
This invention is concerned with a process of converting mixtures of E and Z isomers of certain ketoximes to &gt;98% pure E isomer.
2. Description of the Prior Art
The isomerization of E aromatic aldoximes to Z aldoximes via the hydrochloride salt has been described in Ann. 260, 63 (1890). For example, the E isomer of p-chlorobenzaldoxime (I) was converted to the Z isomer (III) by saturating an ether solution of the E aldoxime with dry HCl and treating the resultant precipitate with sodium carbonate: ##STR1##
Hauser and Hoffenberg have reported, in J.O.C. 20, 1491 (1955), such isomerization utilizing the Lewis acid, BF.sub.3. A benzene solution of the E isomer of p-chlorobenzaldoxime (I) with BF.sub.3 to form a BF.sub.3 complex (IV) and treating with NaHCO.sub.3 solution to obtain the Z isomer (V). ##STR2##
As reported in J. Med. Chem. 20, #9, 1199, (1977) the E isomer of an oximinoether (VI) in diethyl ether was treated with anhydrous HCl. A precipitate was isolated and suspended in water and extracted with ether to yield 37% of the Z isomer VII ##STR3##
It is the surprising discovery of this invention that, contrary to the teaching of the prior art, mixtures of the E and Z isomers of aryl alkyl ketoximes, as contrasted to aldoximes, are converted to 98% E isomer.